An online, double-conversion UPS, a combined power supply and arc quenching device, an electrical appliance and a method of the above type are known in principle. Generally, it is possible that unwanted short circuits or arc faults occur in such an electrical appliance. For example, animals, (wet) dirt or even tools falling onto bare conductors during an inspection can reduce the insulation or the spark gap between two conductors at different voltage potential such that such a fault arc occurs. High arc currents can cause violent explosions because the air in the vicinity of the arc is heated up in a very short time. In electrical low voltage installations, a fault arc is one of the most dangerous forms of a fault that can create a serious hazard for personnel and facilities. Furthermore, long downtime due to excessive damage to equipment, such as electrical distribution panels, may be caused.

Existing solutions to reduce the impact of a fault arc are based on fault arc detection devices that trip the circuit protection devices such as circuit breakers and reduce the time and therefore the energy of the fault arc. Existing methods are focused on cutting off the faulty areas of an electrical appliance from AC mains as fast as possible.

For example, D 199 52 507 A1 discloses a method, in which a fault arc is detected by sensors and as a result switches, in particular, semiconductor switches, are activated and switch a short circuit in order to extinguish the fault arc in a very short time.

Unfortunately, switching devices capable of cutting off very high currents in a very short time are technically complex and very expensive. And whatever efforts are taken, the delay time between the occurrence of a fault arc and switching off the faulty area from the power grid cannot be reduced to zero.